This invention relates to traffic safety equipment, and more particularly to an inertial barrier system for attenuating the energy of errant vehicles.
Inertial highway barriers have been used for some time to prevent vehicles from striking an obstacle such as a bridge pier or the like at full velocity. An inertial barrier relies on the mass of the barrier to decelerate the vehicle. Typically, a dispersible material such as sand is enclosed in a frangible container. When the vehicle strikes the container, the momentum of the impacting vehicle is dissipated in accelerating the sand.
In the current state of the art, standard arrays of sand-filled energy absorbing units are employed, with the amount of sand varying from one barrier unit to the next in a predetermined fashion so that an errant vehicle crashing into the barrier system is decelerated with the minimum damage to the vehicle and its occupants. Because the plastic containers for these units are shatterable if struck at highway speeds, the effect of the barrier on stopping the errant vehicle comes about by transfer of momentum of the vehicle to the sand or other dispersible particulate medium. By arranging the barrier units, in order of striking, from lighter to heavier in terms of amount of sand contained therein, the errant vehicle can be caused to decelerate gradually and with minimum damage to the vehicle and minimum risk to its occupants.
Current standard arrays employ sand containers having weights of 200, 400, 700, 1400, and 2100 pounds. Customarily, spacers or lightweight supports are provided at the base of the barrel so that the center of gravity of the barrier unit is about the same as that of the errant vehicle, i.e. about two feet above the ground. This prevents the errant vehicle from either ramping or climbing over the units on collision or from nosing under the units. Presently, there are three primary methods for elevating the sand mass in a container. A first method, described in U.S. Pat. No. 3,606,258 to Fitch, utilizes a round Styrofoam pedestal or core at the bottom of a container. To obtain barrels having varying weights, the size of the core may be increased or reduced and/or the amount of sand used to fill the void in the barrel not occupied by the core may be varied. A second method, described in U.S. Pat. No. 4,289,419 to B. C. Young, employs an inverted U-shaped plastic support structure disposed at the bottom of the container. As shown particularly in FIG. 7 of that patent, the weight of the containers may be varied by using variously sized plastic support structures or cores to reduce or increase the interior volume of the container which is available for filling with sand.
Yet a third method, which is in primary use today, is described in U.S. Pat. No. 4,688,766 to Zucker. This method employs a plastic disc or core member 20 of a single size, which is supported on a flange disposed on the outer container. When a container having a weight of 200, 400, or 700 pounds is desired, the core is placed within the container in an upside-down configuration, as illustrated in FIGS. 2A-2C of the patent, and the proper amount of sand, according to provided markings, to achieve the desired weight, is introduced into the available reduced volume within the container. When a weight of 1400 pounds is desired, on the other hand, the orientation of the core is reversed, as illustrated in FIG. 3A of the patent, in order to increase the available volume of the container, which is filled with a greater amount of sand. Finally, when a weight of 2100 pounds is desired, as illustrated in FIG. 3B of the patent, the core is removed completely, and the container is completely filled with sand.
Each of the state-of-the art inertial barrier constructions has disadvantages. The system disclosed in the Fitch '258 patent is disadvantageous in that Styrofoam pedestals or cores of differing sizes must be used for each desired weight configuration, and varying levels of sand must be utilized as well. This is labor intensive and relatively complex, involving the maintenance of an inventory of variously sized core elements. Furthermore, the containers all have identical external configurations, regardless of their weight, making ready identification difficult. As a result, external markings, using spray paint, for example, must be utilized to externally identify the weight of a particular container.
The system disclosed in the Young patent '419 is similarly disadvantageous in that plastic support structures or cores of differing sizes must be used for each desired weight configuration, though at least the available volume in each container is filled in each instance, and there is no need to involve road crew personnel in partially filling containers to various levels. Again, the containers all have an identical appearance from the outside, making identification of the particular weight of a container difficult unless it is marked.
The Zucker patent '766 is an improvement over both Fitch and Young, in that only a single sized core is employed for each of the desired weight configurations. However, the system is still disadvantageous in that the exterior appearance of the container is identical no matter what weight configuration is being employed. Additionally, because the sand mass within the container is elevated, in all but the 2100 pound embodiment, and the bottom of the container is tapered, having a smaller diameter than the top portion, the container is hard to move, because it is unstable. Furthermore, if such a container is utilized on uneven ground, the aforementioned tapering can cause bowing of the container wall.
What is needed, therefore, is an impact attenuator configuration having as few pieces as possible, wherein when the sand mass contained therein is elevated, the exterior sidewall of the attenuator container is at least as wide at its bottom portions as it is at its upper portions. Furthermore, it would be advantageous for such a system to be configured so that containers of varying weights have distinctive external appearances, so that the weight of a particular container may be readily discerned by inspecting its external configuration.